PROJECT SUMMARY ABSTRACT Tissue-type plasminogen activator (tPA) is a highly specific serine proteinase present in both the intravascular space and the central nervous system (CNS). In the intravascular space tPA's main role is as a thrombolytic enzyme. Accordingly, recombinant tPA is the only FDA-approved medication for the treatment of patients with acute ischemic stroke. In contrast, the onset of the ischemic insult also induces a rapid rise in the expression and activity of tPA in the abluminal side of the neurovascular unit (NVU) associated with the development of cerebral edema and hemorrhagic transformation. The low density lipoprotein receptor-related protein (LRP) is a member of the LDL receptor gene family that interacts with multiple ligands including tPA. Following the onset of the ischemic insult there is an increase in LRP expression in perivascular astrocytes and the interaction between tPA and LRP in the early phases of the ischemic insult results in the development of cerebral edema. In this application we hypothesize that the interaction between tPA and LRP in perivascular astrocytes is a key molecular mechanism that regulates the barrier function of the NVU. Furthermore we propose that pharmacological inhibition of the interaction between tPA and LRP decreases the incidence of edema and hemorrhagic complications associated with the administration of recombinant tPA for the treatment of acute ischemic stroke. These clinically relevant studies should indicate whether inhibition of tPA-LRP binding in perivascular astrocytes is a successful therapeutic strategy aimed at blocking the deleterious effects of tPA in the abluminal side of the NVU while maintaining its beneficial role as a thrombolytic in the intravascular space.